The present invention relates to prosthetic and orthotic devices and more particularly to a dynamically activated, variable-response prosthetic or orthotic socket system.
An amputee is a person who has lost part of an extremity or limb such as a leg or arm which commonly may be termed as a residual limb. Residual limbs come in various sizes and shapes with respect to the stump. That is, most new amputations are either slightly bulbous or cylindrical in shape while older amputations that may have had a lot of atrophy are generally more conical in shape. Residual limbs may further be characterized by their various individual problems or configurations including the volume and shape of a stump and possible scar, skin graft, bony prominence, uneven limb volume, neuroma, pain, edema or soft tissue configurations.
Referring to FIGS. 1 and 2, a below the knee residual limb 6 is shown and described as a leg 7 having been severed below the knee terminating in a stump 8. In this case, the residual limb 6 includes soft tissue as well as the femur 9, knee joint 10, and severed tibia 11 and fibula 12. Along these bone structures surrounded by soft tissue are nerve bundles and vascular routes which must be protected against external pressure to avoid neuromas, numbness and discomfort as well as other kinds of problems. A below the knee residual limb 6 has its stump 8 generally characterized as being a more bony structure while an above the knee residual limb may be characterized as including more soft tissue as well as the vascular routes and nerve bundles.
Referring to FIG. 2, amputees who have lost a part of their arm 9a, which terminates in a stump 8a also may be characterized as having vascular routes, nerve bundles as well as soft and bony tissues. The residual limb 6 includes the humerus bone 13 which extends from below the shoulder to the elbow from which the radius 14 and ulna 15 bones may pivotally extend to the point of severance. Along the humerus bone 13 are the biceps muscle 16 and the triceps muscle 17 which still yet may be connected to the radius 14 and the ulna, 15, respectively.
In some respects, the residual limb amputee that has a severed arm 9a does not have the pressure bearing considerations for an artificial limb but rather is concerned with having an artificial limb that is articulable to offer functions typical of a full arm, such as bending at the elbow and grasping capabilities. An individual who has a paralyzed limb would also have similar considerations wherein he or she would desire the paralyzed limb to having some degree of mobility and thus functionality.
Historically, artificial limbs typically used by a leg amputee were for the most part all made out of wood such as an Upland Willow. The limbs were hand carved with sockets for receiving the stump of the residual limb. Below the socket would be the shin portion with the foot below the shin. These wooden artificial limbs were covered with rawhide which often were painted. The sockets of most wood limbs were hollow as the limbs were typically supported in the artificial limb by the circumferential tissue adjacent the stump rather than at the distal end of the stump.
Some artificial limbs in Europe were also made from forged pieces of metal that were hollow. Fiber artificial limbs were also used which were stretched around a mold after which they were permitted to dry and cure. Again, these artificial limbs were hollow and pretty much supported the residual limb about the circumferential tissue adjacent the stump.
All of these various artificial limbs have sockets to put the amputee's stump thereinto. There are generally two categories of sockets. There are hard sockets wherein the stump goes right into the socket actually touching the socket wall without any type of liner or stump sock. Another category of sockets is a socket that utilizes a liner or insert. Both categories of sockets typically were opened ended sockets where they had a hollow chamber in the bottom and no portion of the socket touched the distal end of the stump. So, the stump was supported about its circumferential sides as it fits against the inside wall of the sockets.
These types of sockets caused a lot of shear force on the stump as well as had pressure or restriction problems on the nerve bundles and vascular flow of fluid by way of the circumferential pressure effect of the socket on the limb. This lack of contact pressure effect could cause a swelling into the ends of the socket where an amputee may develop severe edema and draining nodules at the end of their stump.
With time, prosthetists learned that by filling in the socket's hollow chamber and encouraging a more total contact with the stump and the socket, the swelling and edema problems could be eliminated. However, the problematic tissue configurations, and bony prominences, required special consideration such as the addition of soft or pliable materials to be put into the socket.
Today, most artificial limbs are constructed from thermoset plastics such as polyester resins, acrylic resins, polypropylenes and polyethylenes, which are perhaps laminated over a variety of textiles which are impregnated by the various resins.
In the past, most artificial limbs were suspended from the amputee's body by some form of pulley, belt or strap suspension often used with various harnesses and perhaps leather lacers. Another method of suspending artificial limbs is known as the wedge suspension wherein an actual wedge is built into the socket which is more closed at its top opening. The wedge in the socket cups the medial femoral condyle or knuckle at the abductor tubical. Yet another form of suspension is referred to as the shuttle system or a mechanical hookup or linkup wherein a thin suction liner is donned over the stump that has a docking device on the distal end which mechanically links up with its cooperative part in the bottom of the socket chamber. Sleeve suspensions were also used wherein the amputee would roll on over both the top of the artificial limb and onto the amputee's thigh. The sleeve suspensions have been used in combination with other forms of suspensions techniques.
Both the use of a positive pressure system and the use of a negative pressure system (or hypobaric closed chamber) have been utilized in the field of prosthetics. At one time, for pressure systems “inflatable inner tubes” were used to fit into sockets. Presently, there are pneumatic “bags” which are strategically placed over what people consider to be good weight-bearing areas to increase pressure to help accommodate for volume changes within the socket.
The problem with this is that higher pressure areas cause more volume losses and this very specific pressure creates atrophy and loss of tissue dramatically over these high pressure areas. None of these systems employs positive pressure distributed over the entire total contact area between the residual limb and the artificial limb socket to accommodate volume changes within the socket.
The negative pressure aspects have been utilized for a closed chamber in that a socket is donned by pulling in with a sock, pulling the sock out of the socket and then closing the opening with a valve. This creates a seal at the bottom and the stump is held into the socket by the hypobaric seal.
The older systems were initially started in Germany. They were an open-ended socket, meaning there was an air chamber in the bottom of the socket. This did not work particularly well because it would cause swelling of the residual limb into the chamber created by the negative draw of suspending the weight of the leg and being under a confined area. This would lead to significant edema which would be severe enough to cause stump breakdown and drainage.
It was later discovered in America that total contact was essential between the residual limb and the socket and once you had total contact the weight was distributed evenly or the suspension was distributed over the whole surface of the limb rather than just over the open chamber portion of the socket.
The use of vacuum to suspend the artificial limb from the residual limb is known and is illustrated in U.S. Pat. No. 6,726,726, herein incorporated by reference.
The human body as a whole is under approximately one atmosphere of pressure at sea level. It keeps and maintains a normal fluid system throughout the body. When an amputee dons a prosthesis and begins taking the pressures of transmitting the weight of the body through the surface area of the residual limb to the bone, there is increased pressure on the residual limb equal to one atmosphere plus whatever additional pressures are created by weight bearing. This increased pressure causes the eventual loss of fluids within the residual limb to the larger portion of the body which is under less pressure. This loss of fluids causes the volume of the residual limb to decrease during the day. It varies from amputee to amputee, but it is a constant among all amputees and the more “fleshy” and the softer the residual limb, the more volume fluctuation there will be. The greater the weight and the smaller the surface area, the greater the pressures will be and the more “swings” there will be in fluids. In the past, the amputee had to compensate for this volume decrease by removing the artificial limb and donning additional stump socks to make up for the decreased residual limb volume.
The human body utilizes a skeletal system to support its mass and weight. None of its remaining systems were designed to support its mass or weight other than the fat pads on the plantar surface of the feet. These fat pads were especially designed to support the weight and mass of the body without losing their fluid content or volume. All remaining tissue is susceptible to loads greater than atmospheric pressure, less than atmospheric pressure, high mechanical pressure, hydration levels, and general vascular and neurological health.
Previous and current socket technologies have always been a rigid support structure that is static in nature and has no way to compensate for limb volume change, changes in tissue load requirements, or concentric or eccentric joint motion which alters the physiological shape of the joint and surrounding soft tissue They have never utilized dynamic response socket technology to compensate for volume and eccentric and concentric joint changes through range of motion of the joint. The utilization of vacuum to date, for example, in U.S. Pat. No. 6,726,726, has only been in the suspension of the artificial limb and has not been utilized in the stabilization and support of vertical tangent and rotational weight bearing loads which are more significant than suspension. For example, the '726 patent discloses vacuum being applied to a cavity between an inner socket and a polyurethane liner to draw the residual limb, encased in the polyurethane liner, against the inner socket to suspend the prosthetic limb from the residual limb. The '726 patent does not, however, disclose the use of a semi-flexible inner socket or a semi-rigid outer socket with a textured surface area available for countering vertical tangent and rotational forces, and accommodating both positive and negative pressures.
Static sockets are unable to compensate for limb volume changes created by loads greater than atmospheric pressure, less than atmospheric pressure, or high mechanical pressure. At present, there is only one item within the confines of the prosthetic socket that has any dynamic response capabilities: a specially formulated urethane interface or liner, also disclosed in U.S. Pat. No. 6,726,726 and incorporated by reference. All other interface media such as TPE or silicone or expanded foam materials do not possess this dynamic characteristic. However, even with this dynamic characteristic, urethane is unable to compensate for many of the socket-created issues.
For example, vacuum's strongest holding force is perpendicular to the surface that it is applied to. About ninety percent of the vertical load forces in a socket are tangent and not perpendicular and therefore vacuum is significantly reduced in its ability to control vertical tangent and rotational loads and distal migration of the limb in the socket. Furthermore, a urethane socket liner has a tendency to flow out of the brim of the socket, and thus become thinner, when subjected to weight-bearing pressures.
An additional problem with laminated sockets is that vacuum leaks out of them, and it therefore necessary for the vacuum to be continually renewed. While sockets of molded thermoplastics do not leak like laminated sockets, and do not absorb moisture, it is difficult to mold the thermoplastic socket with uniform wall thickness.
Skin Physiological Principles
Atmospheric pressure (1 atm=˜14.7 psi) is constantly compressing us from all directions. This may not sound like much, but consider that this compressive pressure over the surface of the average body (˜3,000 in2) totals ˜44,000 lbs of force! The blood and lymphatic vascular systems are well adapted to this large compressive pressure. The tissue pressure throughout our body is only slightly (<0.2%) less than the external atmospheric pressure (Guyton and Hall, Textbook of Medical Physiology). In this pressurized environment the blood capillaries are constantly delivering water and nutrients to all tissues and the blood and lymphatic capillaries remove excess water and wastes from the tissues to sustain a healthy fluid environment in which the cells are bathed.
This homeostatic condition is disturbed when external pressure deviates from 1 atm. The body easily adapts to the daily fluctuations in atmospheric pressure. It can also withstand greater increases or decreases in external pressure for limited amounts of time. However, as seen with amputees, skin health suffers if these deviations from 1 atm are large enough, transition sharply enough or are applied long enough. This is true for pressures above 1 atm and below 1 atm.
For example, high pressures over a bony prominence can cause skin to break down. Sub atmospheric pressure can also lead to skin damage. For example, the distal end of the limb will swell and some of its capillaries rupture if it is leveraged off the bottom of a sealed socket sufficiently hard or for an extended period of time.
Problem Area
With the traditional rigid socket and vacuum suspension, conditions often exist at the brim where the pressures exceed 1 atm and fall below 1 atm.
High Pressure at Brim
The limb experiences high pressure when it is pressed against a rigid brim. This usually occurs under two conditions: 1) the leg leverages in the socket, driving the proximal end of the limb against the edge of the socket brims or 2) the limb slides toward the brim (e.g. wide posterior aspect of the femoral condyles slides forward during knee flexion, wedging it between the narrowing anterior brims). This elevated pressure can lead to ischemia, discomfort, pain, skin breakdown and/or chronic soft tissue atrophy.
Low Pressure
Low pressures at the brim are always due to a slight separation between the liner and skin. This expansion of the trace air space between the skin and the liner decreases pressure between the skin and liner. The skin moves towards the low pressure to fill this space, causing edema and/or dermal capillary bleeding if the pressure drop in the uncontained space is large enough or is applied for an extended period of time.
This space is created by the following sequence of events:
1) The limb and rigid socket are pulled apart (e.g. knee extension leverages the knee away from the rigid brim).
2) This expands the air space between the liner and socket causing a void of low pressure. This is the vacuum space, so it is already under low pressure and the gapping further lowers the pressure.
3) The liner moves towards this low pressure void (towards the socket).
4) As the liner moves towards the socket, it increases the trace space between the liner and skin. This creates a second low pressure space, this one being between the skin and liner.
5) The skin likewise attempts to fill this low pressure void by moving towards the displaced liner.
6) The pressure in the interstitial space (within the soft tissues of the limb), in turn, drops causing greater blood capillary filtration and potential blood capillary rupture. Filtration is leaking of blood plasma (92% water) out of the capillaries and into the interstitial space.
It should be noted in step 3 that the extent to which the liner moves towards the socket will be determined by equilibration of the low pressures in the two voids. When the low pressures in the voids on either side of the liner equilibrate, liner movement will cease.
An example of these steps is illustrated in FIGS. 3 and 4. In FIG. 3, the liner L is in its normal position, “sandwiched” between the limb 6 and rigid socket S. The change in FIG. 4 is that the knee has moved back (A) as the tibia was pressed against the bottom of the socket (B). In this example this occurred because the amputee tried to extend the knee. This leveraging led to the sequence of events listed above, causing low pressure voids at C and D.
When a torque is applied to a traditional rigid socket (S), the socket rotates as it compresses the liner (L) and soft tissues (T) of the leg. On one side of the leg the brim (B) is driven against the limb proximally. This creates a fairly narrow bank of high pressure at the brim. As shown in FIG. 6, when a valgus torque (clockwise in this view) is applied to the socket, the top of the lateral aspect of the socket is driven into the liner and limb, creating a band of high pressure. The pressure is relatively high because of the small surface area (A1) between the top of the socket and liner. Notice that the distal, lateral (D) end of the limb (6) tends to pry away from the socket creating a void V.
The “flexible” inner socket (50) decreases the previously described peak pressures by distributing the brim force over a larger surface area. As shown in FIG. 10, as the brim (78) of the outer socket (70) is driven against the inner socket (50), the inner socket (50) distributes the brim force over a large surface area (A2) of the liner (30). This is much the same principle as a soccer shin guard that has a pliable yet stiff outer shell (equivalent to the inner socket) that when kicked (equivalent to the brim force) distributes the kicking force across the underlying padding (equivalent to the liner) more uniformly to the shin (equivalent to the stump).